1. Field of the Invention
This invention relates to improvements in the fin stock for use in fin and tube heat exchangers, and in particular to achieving improved heat transfer by improved louver patterns therein.
2. Description of the Prior Art
It is well known to use lances through generally planar metal heat exchanger fin stock to displace metal to one side of its plane and thus interfere with and achieve greater heat exchange with the flowing air. Similarly, louvered fin stock may be used. The term "lances" as conventionally used means elongated portions slit and displaced; the term "louvers" means similar portions which are also slanted away from the plane of the fin stock.
For optimum heat exchange efficiency, each portion of the finned heat exchanger should be subjected to air of maximum temperature differential. In the design of louvered stock according to the present invention, this principle is utilized, to the extent feasible, so that the heat exchange capacity of those fin portions subsequent to the first in the line of air flow should not be wasted on air already heated by flow over those first fin portions.
It is conventional to form identical louvers or lances in a progression of identical louvers bent to one side of the plane of the fin stock, with their outstanding edges in a plane parallel to that of the fin stock. In such a progression, only the first louver in the line of airflow encounters the coolest air; after it exchanges heat to the air, that same air, now heated, encounters the subsequent louvers; these function at a reduced temperature differential, with a loss of heat exchange efficiency.
The patent to Seo, Japan, No. 194,194 shows that such a progression of louvers may have both edges of the louvers in planes displaced from but parallel to the plane of the fin stock. Seo's progression is disadvantaged by the same reduced temperature differential for heat transfer.
An extensive theoretical discussion is included in the paper by Kadambi and Giansante, "The Effect of Lances on Finned-Tube Heat Exchanger Performance" 1983, Volume 9, Part 1, American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., Paper No. 2741. Lances or louvers are recognized as increasing the heat exchange of fin stock, though with some increase in power required; and in the Kadambi publication above referred to, it is stressed that their appropriate use will permit greater spacing between fins, and hence the use of less fin stock.